Final answer:
Moderate intensity exercise in the FITT principle should be performed for at least 150 minutes to 300 minutes per week, according to the 2018 Physical Activity Guidelines for Americans.
Step-by-step explanation:
In the FITT principle, moderate intensity exercise should be performed for at least 150 minutes (2 hours and 30 minutes) to 300 minutes (5 hours) per week. This recommendation is based on the 2018 Physical Activity Guidelines for Americans issued by the U.S. Department of Health and Human Services. Moderate activities are those during which a person could talk but not sing, such as brisk walking, swimming, or cycling at a moderate pace.